Today, high-end frequency standard references have relatively high cost, large size, high power consumption, etc. The fast deployment of devices and/or systems such as, but not limited to, global positioning systems (GPS) and/or portable GPS systems, cellular systems and/or portable cellular phones and/or small size and low cost cellular base stations, fast telecommunications systems and other high-speed communication links, which employ very high modulation frequencies require stable, precise and accurate frequency standard reference which have small size, low cost and low power consumption.
Quartz crystals oscillators, on one hand, are the most commonly used local frequency standard, but in many cases are not sufficiently accurate, have long term frequency drift, large size and high power consumption and relatively high cost, in the case of high performance quartz crystal oscillators, these drawbacks prevent them to be suitable for the above applications.
On the other hand Rubidium (Rb) or Cesium (Cs) gas-based atomic clocks are highly accurate and they have high long-term frequency stability. However, the gas-based atomic clocks have large size, high power consumption, and high manufacturing cost.